I have a June 2012 retina macbook pro that has been randomly dying on me recently. It's starting to become more frequent. I will be doing something on my computer and it will just go to a black screen. I press the power button, nothing happens. Press/hold it again and a dead battery logo shows up on the screen. I plug it in, power it back up, and there's 30%+ battery left... Is this normal? I'm assuming it needs a new battery? It's an apple product, so I assume the battery will cost about $300+ and can only be replaced by an apple employee. Any advice? Thanks.